1. Field of the Invention
The present invention relates to an electromagnetic clutch, for transmitting and interrupting a rotational driving force, suitably used to interrupt the operation of a compressor of an air conditioning system of an automobile, etc.
2. Description of the Prior Art
A conventionally known technique for an electromagnetic clutch is disclosed in Japanese Unexamined Patent Publication No. 2000-161389. FIG. 9 is a sectional view of such an electromagnetic clutch 101. In FIG. 9, the left side in the drawing is designated as the front side and the right side in the drawing as the rear side of the electromagnetic clutch 101.
The electromagnetic clutch 101 is mounted on a compressor 110 through an annular support member 109 and comprises an electromagnetic coil 103 built in a stator 102, a rotor 104 freely rotatable around the electromagnetic coil 103, a pulley 114 rotated integrally with the rotor 104 for transmitting the power from the engine not shown, an armature 105 adapted to be attracted to the rotor 104 by the magnetic force generated in the electromagnetic coil 103 and a cylindrical hub 106 adapted to rotate with the armature 105.
The hub 106 is connected to a leaf spring member 111 by a rivet 113. The rear side of the leaf spring member 111 is bonded to the front side of an elastic member 107 by baking. The rear side of the elastic member 107, on the other hand, is bonded to the front side of the armature 105 by baking. The hub 106 is integrally fitted in the rotational direction of a rotary shaft 108 of the compressor by a bolt 112.
The armature 105, which is arranged in an opposed relationship, with a predetermined minuscule gap therebetween, with the friction surface of the rotor 104, is formed of an annular magnetic material such as iron. The rear side of the elastic member 107 is bonded by baking to the front side of the armature 105. By the elastic deformation of the leaf spring member 111, bonded by baking to the front side of the elastic member 107, the armature 105 and the elastic member 107 can be moved along the axial direction of the rotary shaft 108, so that when current flows in the electromagnetic coil 103, the armature 105 is attracted to the rotor 104 by the magnetic force of the electromagnetic coil 103. The impact sound generated at this time by the collision between the friction surfaces of the armature 105 and the rotor 104 is absorbed by the elastic member 107.
Also, once the compressor 110 is “locked”, by foreign matter or otherwise, the armature 105 connected to the hub 106 integrally rotating with the rotary shaft of the compressor 110 also ceases to rotate, and heat is generated by fiction with the rotor 103 still continuing to rotate. This heat is transmitted through the armature 105 to the elastic member 107. As a result, the elastic member 107 is fused, and the armature 105 is separated from the members of the compressor 110 such as the leaf spring member 111, the hub 106 and the rotary shaft 108 which are stopped by the locking of the compressor 110. In this way, the troubles such as a belt being broken or the temperature being abnormally increased due to a protracted overloaded state can be prevented. In other words, the electromagnetic clutch 101 has also the function of a torque limiter.
In the case where the compressor 110 is locked due to foreign matter or otherwise, the torque limiter mechanism of the electromagnetic clutch works to separate the armature 105 from the rotary shaft 108. In the process, the elastic member 107 that has thus far supported the armature 105 is fused. Therefore, the armature 105 is left supported while being attracted to the rotor 104 by the magnetic field generated in the electromagnetic coil 103. As a result, the armature 105 moves in a radial direction by means of a centrifugal force, and this may cause an abnormal noise to be generated by the contact with a rotating inner hub 115.
In the case where the rivet 113 is broken by the overload torque imposed on the electromagnetic clutch 101 before the elastic member 107 is fused by the locking of the compressor 110, the armature 105 moves axially toward the front side of the electromagnetic clutch 101 and may come off.